Resonator fiber optic gyroscopes (RFOG) measure rotation rates by detecting the resonance frequency difference between the light propagating in the clockwise (CW) and counter-clockwise (CCW) directions of a resonator. When the rotation rate of the RFOG is small, the frequency difference is very small. In this case, the back reflected light interferes with the counter-propagating light, which causes large errors in the detection of the rotation rate.
Currently available techniques to overcome this problem use of several different resonance modes to avoid overlap of laser frequencies. Some currently available techniques require more than three lasers to subtract out free spectral range (FSR) fluctuation induced errors. Other currently available techniques use frequency switching techniques to precisely measure and subtract out the FSR. These currently available techniques add complexity and cost to the RFOG.